BT-8

BT-7, BT-7M
BT-7M, 1940, with tracks removed from the wheels and carried on the hull
Type	Light cavalry tank
Place of origin	Soviet Union
Service history
In service	1935–45
Wars	Soviet–Japanese Border Wars, World War II, Winter War
Production history
Designer	Morozov
Designed	1935
Manufacturer	KhPZ
Produced	1935–40
No. built	2,700 - 5,300
Variants	BT-7-1, BT-7-1V, BT-7-2, BT-7A, BT-7M (BT-8), BT-IS
Specifications (variant BT-7-2)
Weight	13.9 tonnes (13.7 long tons; 15.3 short tons)
Length	5.66 m (18 ft 7 in)
Width	2.29 m (7 ft 6 in)
Height	2.42 m (7 ft 11 in)
Crew	3
Armour	Hull: 6-40 mm Turret: 10-15 mm
Main armament	45 mm L/46
Secondary armament	2 x 7.62 mm DT machine gun
Engine	Mikulin M-17T (V-12) gasoline 450 hp (at 1,750 rpm)
Power/weight	32.37 hp/tonne
Transmission	Chain drive (tracks: sliding gear)
Suspension	Christie
Ground clearance	0.305 m (1 ft)
Fuel capacity	360 litres (95 US gal)
Operational range	Road: 430 km (270 mi) Off-road: 360 km (220 mi)
Speed	Road: 72–86 km/h (45–53 mph) Off-road: 50 km/h (31 mph)
Steering system	steering stick

The BT-7 was the last of the BT series of Soviet cavalry tanks that were produced in large numbers between 1935 and 1940. It was lightly armoured, but reasonably well-armed for the time, and had much better mobility than other contemporary tank designs. The BT tanks were known by the nickname Betka from the acronym, or its diminutive, Betushka.

The BT-7's successor was the famous T-34 medium tank, introduced in 1940, which replaced all of the Soviet fast tanks, infantry tanks, and medium tanks then in service.

The first prototypes of the BT-7 had a distinctive canted-ellipse shaped turret mounting both the main gun and a coaxial machine-gun. The specification also called for the project to allow for the installation of new guns without any significant change to the framework: the 76 mm KT-26 or PS-3 main gun (a short-barreled howitzer) and the 45 mm 20K model 1932/38, a long-barreled, high-velocity gun useful against tanks, but less effective than the 76 mm gun against infantry.

In the rear of the turret, there was a rotating drum-type magazine for 18 45 mm shells or a radio station. The prototype underwent an extensive testing program in the summer and autumn of 1934. As a result of this testing, it was felt that a machine-gun was unnecessary on a tank with a 3-man crew, especially as it made the assembly of the turret more complicated.

Therefore, in early 1935, the tank went into production with a simpler design, incorporating the turret from the BT-5. (However, the idea of a wheeled/tracked vehicle with a 76 mm cannon was not abandoned and the plant was commissioned to develop a new BT-7 turret from the turret of the T-26-4.) In the production model, a cylindrical turret housed a 45 mm 20K gun with a DT machine gun. On some of the tanks, a model 71-TC radio with frame antenna was installed.

The crew consisted of three men: the commander (who also served as the gunner); the loader and the driver. In 1937, the company launched production of the BT-7 with a conical turret. The main armament remained the same, but the ammunition was increased to 44 rounds. All serving tanks now installed the DT machine gun in the rear niche. For the firing of the gun and coaxial machine gun at night, the tank was equipped with two special projector-type headlamps, and a mask placed on the gun. Subsequently, these lights were retrofitted to earlier models of the tank. Improvements were also made to the drive wheels, caterpillar tracks and gearbox by 1938.